This invention relates to fasteners for fastening objects to metal channel framing wherein a nut is rotatably mounted in a cage which does not rotate with respect to the channel, said cage clamping the nut crosswise in the channel prior to and during securement of the object to the channel.
Metal framing is commonly used for electrical, mechanical and industrial supports such as for lighting fixtures, pipes and so forth. The framing is formed as a channel having side flanges with opposing, inwardly turned, hook shaped lips defining a slot therebetween. An elongated nut which is narrower and longer than the width of the slot is typically used for securing objects to the framing. As such, the nut is first aligned with the framing and passed through the slot and then turned crosswise with the nut engaging the lips of the channel. An object such as a bracket for a lighting fixture is then locked into position by means of a bolt extending through the object and threaded into a tapped hole in the nut.
A number of different means have been used for holding the nut in the channel in its crosswise position prior to and during securement of an object to the channel. One such means is a coil compression spring on the inside face of the nut which upon insertion of the nut in the slot reacts against the channel bottom and pushes against the channel lips. This arrangement has several serious disadvantages, one being that each channel of different depth requires a spring of correspondingly different length, thus greatly increasing the number of fastener sizes which have to be stocked. In addition, the nuts tend to tilt and topple over into the channel and it is difficult to use the channel as a raceway for wires and the like since the spring substantially blocks the entire channel.
Other prior art means for holding the nut against the channel do not block the channel but they have other drawbacks because they rotate with the nut and slip off the lips of the channel thus causing the nut to fall into the channel. Another problem is that the fasteners tend to be expensive. One example of such means is a coiled spring attached to the outside face of the nut for spanning the slot in the channel and pulling the nut into engagement with the channel lips.
Another means is a cradle for the nut having spring fingers on lugs extending outwardly from the outside face of the nut at opposite ends thereof. The lugs are engageable with the outside faces of the channel lips to pull the nut into engagement with the inside faces of the channel lips upon turning the nut to its crosswise position. The cradle, however, lacks means extending beyond the sides of the nut to prevent it from falling into the channel upon insertion of the nut into the slot.
The fasteners disclosed in U.S. Pat. Nos. 4,146,074, 4,410,298 and 4,460,299 rely upon clamps which rotate with the nut and can slip off the lips of the channel. In addition, the fastener described in U.S. Pat. No. 4,146,074 requires that the sides of the nut be slotted which dictates a separate machining step (e.g. a broaching step) with its attendant costs. The fastener disclosed in U.S. Pat. No. 4,285,379 eliminates the need to slot the nut but the fastener still can slip off the lips of the channel and is difficult to assemble increasing labor costs. The fastener disclosed in U.S. Pat. No. 4,410,298 has no slot but it requires the drilling of a pair of holes.